Vacuum?

6

66Sprinter

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I am running a modded engine with 268 cam, 250 head and valves and all new internals. Using the 1101 from Pony, I have been able to start and drive the car reliably. I dont have any top end..but thats what I except until I get around to opening up the log and adding a 2bbl.

Question...I am getting 12-14" vacuum at idle with this setup? Jon at Pony says I ought to have 17" minimum. With no leaks..I don't know what he bases this on..except the original 200 6cyl. I know that some of you are running even bigger cams (274) so you must have similar vacuum??

Jon seems to point that I have something wrong..(old theme) but the car starts each time, idles, runs and pulls good 1-3. 4& 5y gears are soft since I have no more carb left...

What say you...?

Jim
 
I say your vacuum reading is absolutely normal for the cam and setup you have. My 200 with Clay Smith 264 cam idles at the same vac yours does. Judging by everything I've read here,Jon is not a reliable source of info on anything that is not completely stock.....so bear that in mind.
Sounds to me like your setup is doing exactly what it should be.

Terry
 
Several things contribute to vacuum. Ignition advance and compression are two variables that will affect it a lot.
I think it should have a little more vac than that.
 
I would say you are in the ball park...maybe a hair on the low side, but then again, my vacuum with a 260H Comp Cam is at 15-16" so I wouldn't say you are too far off.

Slade
 
Have you tried adjusting the timing while your vacuum guage is hooked up to see if you can get more vacuum out of it as you advance the timing?
 
All good questions so I will address them in the manner in which I tuned the car.

1st: I have the 250 head with the 1.75" intake bore. I was using the 1.5" to 1.75" adaptor and the 1100 but I could not stop the gas from gyserting out the top. So I am using a 1.75" adaptor and the 1101 which was original to the 250 head.

2nd. Tune up went in this order. Increase idle rpms to 1500. Adj dizzy CCW till I got the best running and faster idel. Turn idle back to 1500. Go to idle mix and adj to reduce mixture until the idel went down. Compensate with more idle RPM. Adj back and forth with idle rpm and mixture until I get the leanest possible. One more time through starting with the dizzy. Reset idle to 1000.

3rd. Go back and tune dizzy to get the most vacuum I can at the idle. Then tweak idle rpm and mixture to stabilize back at 1000. (Its really 1000-1200 because of the lope with the cam. Any lower and she will stall. Any faster is a waist of gas. Check vacuum and again considering the cam lope, I have 12-15" of vacuum. Increase throttle and up the vacuum goes to about 17-20"

4th. Change out plugs (at least two of them new) and go for a test drive about 15 mins at 70mph. Pull over and out come the new plugs for a look see. They are dark but not sooty. I am guess just above normal for richness.

Last problem I have is the one that requires a larger intake and bigger carb. I was just curious about the vacuum reading. Of course, common sense says if it starts, runs, stops and does what you ask..no problem.

I was considering an O2 sensor, but will wait until I do the log mods and new carb. Interesting what I have heard so far. I hope to upload a recent video on CAR DOMAIN. I am chasing down a Mercedes SL roadster in St. Louis. We got up to 85 then he backed up. I really wasn't on it too hard..but you can hear me call the gears to my wife as she holds the camera.
 
My 78 stock engine, except for a 4° advanced timing chain with a C4 and no emissions stuff except for EGR, manual brakes, no A/C pulls a steady 14".
 
Yup...I just wanted to check and see if mine was an oddball or just normal. Appreciate the feedback...I was unable to post the video chasing the SL Roadster..(103MB is the file and Domain only allowed uploads of 100MB max!) but I put two others on..I will put a link in once they're done.
 
I have 15" in park @ 1000 rpms
11" in drive. Bill
 
I have my PCV connected at the carb adapter, and reads 16" at idle in Park.
The Power Brake Booster, Trans Modulator and Cruise Control are at the Manifold, and read 18" at idle in Park.
The Ported Vacuum at the base of the carb reads 0" at idle, and 22" max at 2000 RPM +.
HWVac13.jpg
 
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